Asymmetric shaped charges and method for making asymmetric perforations

ABSTRACT

There is a shaped charge for making an asymmetrical perforation into a casing. The shaped charge includes a case extending along a symmetry axis X and having a back wall and an open end; an explosive material located within the case; a liner located within the case, over the explosive material; a booster material; and an asymmetrical feature. The asymmetrical feature is selected to generate an asymmetrical perforation into the casing.

BACKGROUND Technical Field

Embodiments of the subject matter disclosed herein generally relate to shaped charges and associated perforations made in the casing of a well, and more specifically, to methods and systems for generating an asymmetric jet of material for perforating the casing to obtain a desired perforation profile.

Discussion of the Background

In the oil and gas field, once a well 100 is drilled to a desired depth H relative to the surface 110, as illustrated in FIG. 1, and the casing 102 protecting the wellbore 104 has been installed and cemented in place, it is time to connect the wellbore 104 to the subterranean formation 106 to extract the oil and/or gas. This process of connecting the wellbore to the subterranean formation may include a step of plugging a previously fractured stage of the well with a plug 112, a step of perforating a portion of the casing 102, corresponding to a new stage, with a perforating gun string 114 such that various channels 116 are formed to connect the subterranean formation 106 to the inside of the casing 102, a step of removing the perforating gun assembly, and a step of fracturing the various channels 116 of the new stage. These steps are repeated until all the stages are fractured.

During the perforating step for a given stage, perforating guns 115 i of the perforating gun string 114 are used to create perforation clusters in the horizontal multistage hydraulically fractured unconventional well 100. Clusters are typically spaced along the length of a stage 140 (a portion of the casing that is separated with plugs from the other portions of the casing), and each cluster comprises multiple perforations (or holes) 130. Each cluster is intended to function as a point of contact between the wellbore 104 and the formation 106. After each stage 140 is perforated, a slurry of proppant (sand) and liquid (water) is pumped into the stage at high rates and then, through the perforation holes 130, into the formation 106, with the intent of hydraulically fracturing the formation to increase the contact area between that stage and the formation. A typical design goal is for each of the clusters to take a proportional share of the slurry volume, and to generate effective fractures, or contact points, with the formation, so that the well produces a consistent amount of oil cluster to cluster and stage to stage.

In typical wells, the distribution of the slurry and proppant between the various clusters is not uniform. There can be more slurry deposited near the toe end 140A of the stage 140, resulting in a toe biased stage, or more deposited near the heel end 140B of the stage 140, resulting in a heel biased stage. Sometimes, the clusters may not take appreciable amounts of slurry at all. Size, shape, distribution, and uniformity of perforation holes may contribute to this treatment nonuniformity.

The perforation geometry is typically a round hole 130, as shown in FIG. 2, punched at a 90 degree angle to the well axis X. During the fracturing treatment, holes that are taking fluid and sand may erode to new shapes 132, as the sand wears against the perforation hole while turning from moving down the well and into the perforation hole. This process is exaggerated if only a few of the holes in the stage are taking the slurry, and the eroded holes continually take more fluid, thus propagating the effect even further as the eroding hole 132 becomes much larger than all of the other holes 130 in the stage.

Constant Entry Hole or Equal Entry Hole (CEH or EEH) charges have proven to be very beneficial in this application. Baseline conventional shaped charges 150 (FIG. 3 shows two shaped charges of the gun 115 i, one 150 oriented downward and one 152 upward) tend to create a much larger hole 151 in the short water gap G1 when the gun 115 i rests on the low-side 102A of the casing 102 and a much smaller hole 153 in the high-side 102B of the casing 102 through the longer water gap G2. This means that the water gap negatively affects the size of the holes made in the casing by the shaped charges. The larger holes 151 take more fluid than the smaller holes 153, and they erode over time, resulting in the large holes taking eventually all of the fluid. CEH charges promote more uniform distribution of fluid, and allow the overall reduction of the nominal hole size, which further enables high-density perforation techniques.

One mechanism to promote a more equal distribution of the slurry into the hole is the SANDIQ system, belonging to the assignee of this application, in which the perforation charges with CEH or Constant Entry Hole design are angled toward the toe so as to create a perforation which might more readily accept fluid and sand with less erosion, and with a lower pressure drop. Field results have been promising, with lower pressure drops observed during treatment, and hinting that the discharge coefficient might be higher than with systems having shaped charges with no angle.

Shaped charges which create slots have also been used to create noncircular perforation tunnels. These charges have been used in arrangements where the slot was perpendicular to the well axis (as shown in FIG. 2 for slot 132) for the purpose of plug and abandonment (channel finding), and at an angle to the axis for fracturing in vertical wells (Saber jet technology). The slots have been generated through nonuniformity in the casing, or as a modular linear charge that has been shortened for use in perforating guns. Slot based charges have the disadvantage that the resultant jet is spread over a broad area, resulting in extreme sensitivity to the water gap in the pressurized well. Slot creating perforators therefore would create a large variation in the hole size in the horizontal wells, which would be disadvantageous for this application. Further, slot perforators have not been developed in systems where the slots are oriented in line with the well axis so as to provide beneficial proppant and fluid transport from the well to the formation during hydraulic fracturing operations.

Thus, there is a need to form slots into the casing, to control an orientation of the slots along the casing, and to design shaped charges that would achieve these results on a consistent basis.

SUMMARY

According to an embodiment, there is a shaped charge for making an asymmetrical perforation into a casing. The shaped charge includes a case extending along a symmetry axis X and having a back wall and an open end; an explosive material located within the case; a liner located within the case, over the explosive material; a booster material; and an asymmetrical feature. The asymmetrical feature is selected to generate an asymmetrical perforation into the casing.

According to another embodiment, there is a liner for covering an explosive material in a case of a shaped charge. The liner includes a metallic powdered material, a binder that holds together the metallic powdered material, and an insert located partially within the metallic powdered material. The liner has a concave shape.

According to still another embodiment, there is a shaped charge for making an asymmetric perforation in a casing of a well. The shaped charge includes a case extending along a symmetry axis X and having a back wall and an open end, an explosive material located at the back wall of the case, a liner located within the case, over the explosive material, and a booster material located in a channel formed in the back wall of the case. The liner includes a metallic powdered material; a binder that holds together the metallic powdered material; and an insert located partially within the metallic powdered material. The liner has a concave shape.

According to yet another embodiment, there is a gun for perforating asymmetrically a casing of a well. The gun includes a gun carrier; and a shaped charge located inside the gun carrier and having a liner placed over an explosive material, where the liner includes a metallic powdered material; a binder that holds together the metallic powdered material; and an insert located partially within the metallic powdered material. The liner has a concave shape.

According to another embodiment, there is a method for making a shaped charge that is capable of making an asymmetric perforation into a casing. The method includes providing a case that extends along a symmetry axis X and has a back wall and an open end; making a channel through the back wall; installing a booster material into the channel; adding an explosive material to the back wall of the case; forming a liner; and placing the liner within the case, over the explosive material. The shaped charge has an asymmetrical feature selected to make the asymmetric perforation into the casing.

According to another embodiment, there is a gun for perforating a casing in a well. The gun includes a gun carrier and an asymmetric shaped charge located inside the gun carrier. The shaped charge has an asymmetrical feature selected to make an asymmetric perforation into the casing.

According to another embodiment, there is a casing that was perforated with an asymmetrical shaped charge. The casing includes a round wall; and an elongated perforation formed in the round wall with the shaped charge. A longitudinal axis x2 of the elongated perforation extends along a desired direction as a result of using the asymmetrical shaped charge.

According to another embodiment, there is a method for making an asymmetrical perforation in a casing. The method includes lowering a gun into the casing of a well; firing an asymmetric shaped charge located inside a gun carrier of the gun; and forming the asymmetrical perforation in the casing due to the asymmetric shaped charge.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:

FIG. 1 illustrates a well and associated equipment for well completion operations;

FIG. 2 illustrates various holes formed in a casing due to shaped charges;

FIG. 3 illustrates how the size of the holes made in the casing is influenced by the water gap between the casing and the gun;

FIG. 4 illustrates an asymmetrical shaped charge having a tilted liner;

FIG. 5 illustrates an asymmetrical shaped charge having an asymmetrical channel and booster material;

FIG. 6 illustrates an asymmetrical shaped charge having two asymmetrical channels;

FIG. 7 illustrates an asymmetrical shaped charge having an explosive material with a varying characteristic;

FIG. 8 illustrates an asymmetrical shaped charge having an insert;

FIG. 9 illustrates an asymmetrical shaped charge having an insert with a window;

FIG. 10 illustrates an asymmetrical shaped charge having an insert attached to a liner;

FIG. 11 is a top view of the asymmetrical shaped charge having the insert attached to the liner;

FIG. 12 illustrates the distribution of the initiation points;

FIG. 13 illustrates an asymmetrical shaped charge having an asymmetrical case;

FIG. 14 is a flowchart of a method for making an asymmetrical shaped charge;

FIG. 15 illustrates a liner having an insert completely embedded into the liner;

FIG. 16 illustrates a liner having an insert asymmetrically embedded into the liner;

FIG. 17 illustrates a liner having an insert flush with a surface of the liner;

FIG. 18 illustrates a liner having an insert and a certain profile;

FIGS. 19A to 19D illustrate various perforations that may be made in a casing with one or more of the shaped charges discussed herein;

FIG. 20 is a flowchart of a method for making a liner as illustrated in one of the FIGS. 15-18; and

FIG. 21 illustrates a gun that has one or more of the shaped charges discussed herein.

DETAILED DESCRIPTION

The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a perforating gun used for perforating a casing in a well. However, the embodiments discussed herein may be used for guns in another context.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

According to an embodiment, a shaped charge includes a case, an explosive material, a liner, and a booster material. The explosive material is sandwiched between the case and the liner and the booster material is in contact with the explosive material, at one edge of the explosive material. At least one of these elements of the shape charge is made to be asymmetrical regarding a longitudinal axis (symmetry axis) of the shaped charge. In one variation, although all the above elements of the shaped charge are symmetrical relative to the symmetry axis, one or more inserts are added to one or more of these elements and the insert is made asymmetrical. For example, the insert may be asymmetrical in shape relative to the longitudinal axis. However, in one application, the insert may have a symmetrical shape, but asymmetrical properties, i.e., different physical properties as, for example, a melting point, impedance, etc. In one application, the insert is made of an inert material, i.e., a material that does not explode, ignite, or burns under natural conditions. These possible implementations of an asymmetrical shaped charge are now discussed.

A shaped charge 400 is illustrated in FIG. 4 as having a case 402. Case 402 may be made of any material that is strong enough to resist when the explosive material explodes. For example, the case may be made of steel or a metal. The case may take any shape, for example, conical, cylindrical, spherical, hemispherical, bell-shaped, parabolic or hyperboloid. FIG. 4 shows the case 402 having a cup shape, with a solid back wall 404 having a channel 406 in which the booster material 430 is located. The back wall 404 is also called herein a closed end. A pedestal 405, which is attached to the back wall 404 (made either integrally or separately of the pedestal) is used to attach the shaped charge to a carrier (not shown) in the gun and affix the detonation cord. The channel 406 may extend through the pedestal 405, along the symmetry axis X. The back wall 404 continues with a side wall 408 that is shaped as a cup. A top 409 of the case 402 is open. For this reason, this part of the case is called an open end.

An explosive material 410 is placed inside the cup shaped case 402. The explosive material 410 is typically packed inside the case 402 by micro-forging or other methods. The explosive material may be a high explosive material, like NONA, ONT, RDX, HMX, HNS, BRX, PETN, CL-20, HNIW, PYX, TATB, TNAZ, HNIW, or other known explosive. The liner 420 covers the explosive material 410 and keeps it inside the case 402. The liner 420 may be made of a reactive or an inert material, e.g., metal particles mixed with a light glue, so that the liner appears like a metallic sheet.

The booster material 430 is placed at the bottom of the case 402, in the channel 406. The booster material 430 is connected to a detonation cord 440, which initiates the detonation of the booster material 430. The booster material includes a detonation material, which may be the same as the explosive material 410 or different. When the gun is fired, the gun detonator is first detonated, which initiates the detonation cord 440. The detonation cord 440 initiates the booster material 430. The detonation of the booster material 430 starts the explosion of the explosive material 410. Thus, in the embodiment of FIG. 4, there is a single initiation point, at the interface between the booster material 430 and the explosive material 410. The explosive material 410 is then initiated, which generates a detonation wave. The detonation wave collapses the liner 420 and melts it at the same time, resulting in a jet of material, which is expelled from the case 402 through the open end 409 with a high energy. If the arrangement of the elements shown in FIG. 4 is symmetrical relative to the longitudinal axis X (the terms “longitudinal axis X” and “symmetry axis X” are used herein interchangeably), then the jet has substantially a circular cross-section and would generate substantially a circular hole in the casing of the well.

However, in the embodiment of FIG. 4, the liner 420 is not made to be symmetrical to the longitudinal axis X. As shown in the figure, the case 402 extends along the longitudinal axis X up to a height having the coordinate x1. One side 420A of the liner 420 extends to a height having the coordinate x2 (which may be the same or smaller than x1) and the opposite side 420B of the liner 420 extends to a height having the coordinate x3, which is different from coordinate x2. This means that the liner 420 is tilted relative to the case 402 and the symmetry axis. If the symmetrical reference position 422 of the traditional liner relative to the symmetry axis X is considered to correspond to a zero angle, the tilted novel liner 420 can make any non-zero angle θ with the reference position. In one application, it is possible that the liner has its own symmetry axis X′ and the entire liner is tilted so that the symmetry axis X′ makes the non-zero angle θ with the symmetry axis X. However, in another embodiment, only a portion of the liner is tilted while the remaining part of the liner is not tilted, so that the liner itself has no symmetry axis. Irrespective of how the non-symmetrical liner is implemented, the non-symmetry of the liner would also make the explosive material 410 to be not symmetric relative to the longitudinal axis X.

In another embodiment illustrated in FIG. 5, the explosive material 410, the liner 420, and the case 402 are all symmetrical relative to the longitudinal axis X. However, the booster material 430 is not symmetrical. FIG. 5 shows that the channel 506 is formed to extend along a longitudinal axis X″, which makes a non-zero angle α with the symmetry axis X. Note that in the embodiment of FIG. 4, the longitudinal axis X and the axis X″ would have been coincident if axis X″ would have been shown there. In other words, the channel in FIG. 5 has a longitudinal axis X″, which makes a non-zero angle with the symmetry axis X. This means that the booster material fires along an axis that is not the symmetry axis X. In one application, the booster material fires toward a side wall 408 of the case 402.

As previously discussed, the booster material 430 constitutes the initiation point for the explosive material. Due to the asymmetry of the booster material, the propagation of the detonation front becomes also asymmetrical inside the explosive material 410 while inside the case 402, which results in the expelled jet being non-symmetrical. As will be discussed later, by controlling the asymmetry of the shaped charge, the expelled jet is expected to form a key hole shape in the casing or a slot with a desired orientation relative to a longitudinal axis of the casing of the well.

In one embodiment, it is possible to combine the asymmetric features shown in FIGS. 4 and 5, i.e., to have a shaped charge with a tilted liner and the booster material oriented away from the symmetry axis X of the case.

According to another embodiment, as illustrated in FIG. 6, the channel 606 is physically offset from the symmetry axis X, with a given distance d. In this way, the channel 606 is asymmetrically positioned relative to the symmetry axis X and/or the case 402, so that the generated jet is expected to form a key hole or slot shape into the casing of the well. In still another embodiment, the channel 606 axis X″ may make a non-zero angle with the symmetry axis X, similar to the embodiment shown in FIG. 5, except that the channel 606 is also offset from the symmetry axis X. In yet another embodiment, one or more additional channels 606′ may be formed in the base wall 404, also offset from the symmetry axis X. The additional channel 606′ extends along its own longitudinal axis X′″, which may be parallel to axis X″ of channel 606, or they may make a non-zero angle. In one application, the two channels 606 and 606′ are located asymmetrically relative to the symmetry axis X, as shown in FIG. 6. In still another application, one of the channels 606 and 606′ is oriented to have the longitudinal axis parallel to the symmetry axis X while the other channel makes a non-zero angle with the symmetry axis X. Any other variation of these arrangements that achieves a non-symmetrical jet may be used, for example, combining one or both of the embodiments illustrated in FIGS. 4 and 5 with this embodiment.

According to another embodiment, which is illustrated in FIG. 7, the explosive material 410 is made to have at least two different volumes 712 and 714 that differ from each other in one characteristic. The volumes may have any shape, may be the same or different, as long as an asymmetry in the generated jet is achieved. The characteristic may be the chemical composition, density, electrical impedance, strength, thermodynamic stability, etc. This embodiment may be combined with one or more of the previously discussed embodiments to further control the asymmetry of the generated jet.

In another embodiment, as illustrated in FIG. 8, an insert 800 is added to the shaped charge to achieve the desired asymmetry. The insert 800 may have any shape, may be made of ferrous, inert or composite materials, may have any thickness and may be positioned anywhere inside the explosive material 410 as long as it generates an asymmetry in the detonation wave, to obtain a controlled asymmetrical jet. Although the insert 800 is shown in FIG. 8 as being placed in one half of the case 402, it is possible to place the insert to extend in both halves of the case. Also, the thickness of the insert does not have to be constant as illustrated in the figure. The insert 800 is not placed to separate the explosive material 410 from the booster material 430.

In one variation of the embodiment of FIG. 8, the insert is attached to the case 402, either as insert 810 to the wall 408, or as insert 820 to the back wall 404. In still another application, an insert 830 may be placed inside the channel 406. In one embodiment, one or more of the inserts 800, 810, 820, and 830 may be located inside the case 402. One or more of the inserts 800, 810, 820, and 830 may have a window 802 cut into it, as illustrated in FIG. 9, which shows a top view of the shaped charge 400. Th inserts discussed herein may be combined in any way.

In another variation of the embodiment of FIG. 8, the insert may be attached to the liner 420 as illustrated in FIG. 10 (see element 1000). The insert 1000 may be made of metal, ceramic, polymer or other materials. Similar to the embodiments of FIGS. 8 and 9, the insert 1000 may have any shape, thickness or may have a window. The insert 1000 may directly deposited on the liner with a 3D printer. In one application, the insert 1000 is achieved by painting the back of the liner 420 with a thick bead substance, for example, glyptol, glue, epoxy, or other polymers. In still another application, the insert 1000 may be a pocket of air or air trapped within a printed or foamed material. The insert 1000, similar to the insert 800, may be attached to only a sector of the liner 420, or all around the liner as illustrated in FIG. 11, which shows a top view of the liner. While FIGS. 10 and 11 shows the formation of the insert 1000 on the back of the liner, i.e., between the liner and the explosive material 410, it is also possible to form the insert on top of the liner, on the opposite side of the explosive material. Note that the various asymmetric features discussed in the previous embodiments may be combined in any way.

For any of the above discussed embodiments, if two inserts 1200 and 1210 are used, they may be distributed inside the case 402 so that an angle β between the two inserts is in the range of 165 to 195°, as illustrated in FIG. 12. In this way, a variable initiation profile in the initiation section (i.e., booster material) of the shaped charge is obtained, which is responsible for the generation of an asymmetric detonation wave front, which ultimately results in the asymmetric jet. This asymmetric jet then creates the key hole and/or slots in the casing of the well. The inserts discussed above can be made, not only of metallic, polymer or plastic materials, but also from ceramic, e.g., silica sand.

In still another embodiment, as illustrated in FIG. 13, it is possible to make the case 402 to be asymmetrical. The wall 408 is made to have a part 408A having a first shape and another part 408B having a different shape. The shape is directly associated with the volume of explosive material 410 held by the respective part. For example, FIG. 13 shows the part 408A of the wall being shaped to hold less explosive material 410 than the wall part 408B. The same is true for the parts 404A and 404B of the back wall. Note that channel 406 still extends along the former symmetry axis X, which is not a symmetry axis for this embodiment.

The liner 420 has a smaller part 422 that corresponds to the smaller volume of explosive material hold by the part 408A of the lateral wall 408 and a larger part 424 corresponding to the part 408B. Thus, for the embodiment shown in FIG. 13, each of the case 402, the liner 420, and the explosive material 410 are asymmetrical relative to the symmetry axis X. In one modification of this embodiment, it is possible to make the liner 420 and the explosive material 410 symmetrical relative to an axis X′ parallel to symmetry axis X. Further, in another modification, it is also possible to tilt the liner, or to implement any of the asymmetries discussed above with regard to FIGS. 4-12.

A method for manufacturing an asymmetrical shaped charge 400 (as shown in any of the FIGS. 4-13) is now discussed with regard to FIG. 14. In step 1400, a case 402 is provided. The case 402 may have a symmetry axis X, which is also a longitudinal axis. However, the case may also be asymmetric. In step 1402, the channel 406 is made into the back wall 404 of the case 402. The channel 406 may be made along the symmetry axis X, inclined relative to this axis, or offset from the symmetry axis. If the channel 406 is made offset from the symmetry axis X, it may also be made to extend along an axis X″ that is parallel to the symmetry axis X, or axis X″ makes a non-zero angle with the symmetry axis X. In one embodiment, more than one channel 406 is formed into the back wall 404 of the case 402, so that all these channels are asymmetrically distributed relative to the symmetry axis X.

In step 1404, the booster material 430 is placed into the channel 406 by any known method. If more than one channel 406 is formed, the channels may be distributed as illustrated in FIG. 12, to achieve a desired angle between the initiation points. In step 1406, the explosive material 410 is added to the interior of the case 402. The explosive material can be added by any known means. The explosive material 410 may be made to be uniform or not. If the explosive material is not uniform, at least one characteristic of the explosive material may vary inside the case, as discussed above with reference to FIG. 7. In one application, another material may be inserted at specific locations inside the case to vary the characteristic (e.g., density, explosive strength, flammability) of the explosive material. The another material may be the insert 800 or 1000 discussed above, or even air or another inert material. The explosive material 410 may be made to be symmetrical or not relative to the symmetry axis X. The symmetry refers to the volumetric distribution of the explosive material, or to at least another characteristic (as discussed above) of the explosive material.

In step 1408 the liner 420 is formed. The liner may be formed by injection mold, 3D print, machined, cast, extrusion, stamping, mold, microforge, etc. The liner 420 may be made to be symmetric relative to the symmetry axis X or not. In one embodiment, one side of the liner is made larger than the other side of the liner, as illustrated in FIG. 13. In one application, the liner is shaped as a trumpet for directing the explosive energy to a desired location. In optional step 1410, an insert 1000 may be attached to the liner as illustrated in FIG. 10. Alternatively, an insert 800 may be added to the explosive material 410 or the case 402 as illustrated in FIG. 8. In still another application, the insert may be added to the channel 406, to make the entire shaped charge asymmetrical, as shown in FIG. 8. Step 1410 may be performed at any time during the method, depending where the insert is placed. Finally, in step 1412 the liner is attached to the case so that the shaped charge is ready to be used.

In the above discussed embodiments, the asymmetry of the shaped charge has been added to one of the elements of the shaped charge. However, it is possible to introduce an asymmetry into the structure of the liner itself. Thus, the next embodiments discuss these possibilities. FIG. 15 shows a liner 420 disposed symmetrically around the symmetry axis X. However, different from the previous embodiments, an insert 1500 is located completely within the liner 420, i.e., no face or edge of the insert 1500 is facing the explosive material 410 or the ambient above the shaped charge 400. The insert 1500 may be made of the same materials as the inserts 800 and 1000, and it may be manufactured by forging, molding, or printing. The insert 1500 may be symmetric relative to the symmetry axis X, extends along the liner 420, but not over the entire liner so that a central portion 426 of the liner 420 has the insert and a peripheral portion 428 of the liner is free of the insert. Thus, in this embodiment, both the liner 420 and the insert 1500 are symmetrical relative to the symmetry axis X, but the asymmetry of the shaped charge is achieved because the insert does not extend over the entire liner.

The liner 1500 (and other liners illustrated in other figures) may have a generally concave shape. The concave shape may be symmetrical or not relative to the symmetry axis X. The concave shape may be implemented in many ways, for example, as a trumpet, cone, bell, hemispherical, etc. The liner 420 includes at least one type of powdered metal 1502. The metal may be copper, tin, nickel, tungsten, lead, molybdenum or a combination of these materials. The metallic powder is held together with a binder 1504. The binder can be a glue, polymer or other material. In one application, the liner is machined from a solid piece of material. In another application, the liner is printed, forged, or molded.

In another embodiment illustrated in FIG. 16, an insert 1600 is located only in one portion of the liner and not in an opposite portion. Thus, the asymmetry of the shaped charge is achieved in this embodiment because of the location of the insert within the liner. The asymmetry shown in either FIG. 15 or FIG. 16 may be combined with any of the previously discussed asymmetries of the shaped charge.

The embodiment of FIG. 17 is similar to that of FIG. 16, except that a face 1700A of the insert 1700 is fully exposed either to the ambient or to the explosive material 410, i.e., a face of the insert is flush with a front or back face of the liner 420.

The embodiment illustrated in FIG. 18 shows the liner 420 having the insert 1800 distributed according to any of the embodiments of FIGS. 15-17, but an angle γ between the symmetry axis X and an arm of the liner is between 20 and 40°, or between 100 and 120°.

Any of the configurations discussed above achieves a jet of material that is not symmetrical. Based on experiments performed by the inventors, one or more of these asymmetrical configurations may generate the following holes in a casing. FIG. 19A shows a part of a casing 1902 that extends along a longitudinal axis X2, which coincides with the longitudinal axis X1 of the well. A slot 1910 is formed in the casing with one of the above shaped charge configurations. The slot 1910 extends along the longitudinal axis X1 due to the orientation of the asymmetry of the shaped charge. The slot 1910 is defined as having a middle portion 1912 that has the largest size along an axis Y1 perpendicular to the longitudinal axis X1, and two end portions 1914 and 1916 that narrow when moving away from the middle portion 1912.

FIG. 19B shows a key hole perforation 1920 formed in the casing 1902. The key hole perforation 1920 is defined as having a head portion 1922 that is substantially circular, and a tail portion 1924, that has a decreasing size. The key hole perforation 1920 was made so that it extends along the X2 axis, with its head portion closer to a heel of the casing (when the casing is used in a horizontal well) so that the pumping of the slurry does not erodes substantially this portion. In this embodiment, the shaped charge is selected to have the longitudinal axis X2 of the key hole aligned with the longitudinal axis X1 of the casing.

By changing the orientation and/or location of the asymmetry in the shaped charge, it is possible to control the position of the longitudinal axis X2 of the slot 1910 or key hole 1920. For example, as shown in FIG. 19C, four key holes 1930-1 to 1930-4 are formed so that their head portions are substantially superimposed and their tails are distributed as the spokes of a wheel. For obtaining such a configuration, four different shaped charges are used. After the first key hole 1930-1 is made with a first shaped charge, the gun is moved so that a second shaped charge is aligned with the head portion of the first key hole. As the second shaped charge is rotated relative to the first shaped charge, i.e., the initiation point(s) of the first shaped charge are angularly offset from the initiation point(s) of the second shaped charge, the second shaped charge forms the second key hole 1930-2. The process continues until all four shaped charges are fired and the configuration shown in FIG. 19C is obtained. More or less than four shaped charges may be fired at the same location of the casing for obtaining a star configuration or a triangle configuration, or other configurations.

FIG. 19D shows a configuration in which a slot 1940 and two key holes 1950-1 and 1950-2 are formed to have a common area 1942. Similar to the embodiment of FIG. 19C, more or less shaped charges may be used to obtain different perforation configurations.

For all the embodiments discussed herein, while the asymmetric shaped charges may be attached to the gun carrier to be perpendicular to the longitudinal axis of the casing, it is also possible to have the shaped charges installed with a non-zero angle relative to the axial direction of the casing. In one embodiment, it is possible that some asymmetrical shaped charges are perpendicular to the longitudinal direction of the casing while the other asymmetrical shaped charges are tilted to the axial direction. Further, in one application it is possible to combine traditional, symmetrical, shaped charges with one or more of the novel asymmetrical shaped charges discussed above.

One advantage of making key hole perforations is that it can be made in a consistent manner. Traditional slot charges are very sensitive to the water gap and pressure, and will produce suboptimal results in downhole conditions. The key hole perforation produced with the asymmetrical shaped charge discussed above has a consistent hole size, with the key hole extending the opportunity for sand placement.

Another possible advantage is that the traditionally eroded holes tend to be shaped like a key hole, so that by directly producing a key hole perforation, it is likely to be less eroded by the sand placement.

In one embodiment, the perforations will be a tapered slot, generated by a slot producing charge being held at an angle within the gun body (generally tilted toe-ward, but could be either way) so that the travel distances for the various parts of the jet are not symmetric, which will result in a narrowing slot.

A method for making the liner shown in FIGS. 15-18 is now discussed with regard to the flowchart illustrated in FIG. 20. In step 2000, the material for an insert 1500, 1600, 1700 or 1800 is selected. In step 2002, the insert is made into the desired shape. Any known method that is used for making the liner may be used to form the insert. Then, in step 2004, the insert is positioned at one of the positions shown in FIGS. 15-18, inside the material of the liner, and in step 2006 the material of the liner is pressed (other methods may be used) to create the liner. Note that at least a first face of the insert is fully embedded within the liner as illustrated in any of the embodiments of FIGS. 15-18. In one embodiment, at least a second face of the insert is partially, if not totally embedded within the liner. In some embodiments, more than two faces (even all the faces) of the insert are fully embedded into the liner. In still another embodiment, only one face is not fully embedded into the liner.

A gun having one or more of the shaped charged discussed with regard to FIGS. 4-20 is illustrated in FIG. 21. Gun 2100 includes a gun carrier 2110 that houses one or more shaped charges 400. The gun carrier may be shaped as a cylinder and may be sealed from the casing of the well. A first shaped charge 400 has its symmetry axis X making a non-zero angle with a radial axis Y, which is perpendicular on the longitudinal axis L of the gun carrier. However, a second shaped charge 400 is shown having its symmetry axis X making a zero angle with the radial axis Y. Any number of shaped charges 400 may be positioned within the gun carrier. In one embodiment, traditional shaped charges 150 (discussed with regard to FIG. 3) are mixed up with the asymmetrical shaped charges 400.

The disclosed embodiments provide methods and systems for generating a slot or key hole perforation into a casing of a well, by using at least a shaped charge that has an asymmetrical feature. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims. 

1. A liner for covering an explosive material in a case of a shaped charge, the liner comprising: a metallic powdered material; a binder that holds together the metallic powdered material; and an insert located partially within the metallic powdered material, wherein the liner has a concave shape.
 2. The liner of claim 1, wherein the insert is fully immersed within the liner.
 3. (canceled)
 4. The liner of claim 1, wherein the insert is asymmetric relative to a symmetry axis of the liner. 5-7. (canceled)
 8. The liner of claim 1, wherein one face of the insert is flush with a surface of the liner and the remaining of the insert is fully embedded into the liner.
 9. (canceled)
 10. A shaped charge for making an asymmetric perforation in a casing of a well, the shaped charge comprising: a case extending along a symmetry axis X and having a back wall and an open end; an explosive material located at the back wall of the case; a liner located within the case, over the explosive material; and a booster material located in a channel formed in the back wall of the case, wherein the liner includes: a metallic powdered material; a binder that holds together the metallic powdered material; and an insert located partially within the metallic powdered material, wherein the liner has a concave shape. 11-27. (canceled)
 28. A shaped charge for making an asymmetrical perforation into a casing, the shaped charge comprising: a case extending along a symmetry axis X and having a back wall and an open end; an explosive material located within the case; a liner located within the case, over the explosive material; a booster material; and an asymmetrical feature, wherein the asymmetrical feature is selected to generate an asymmetrical perforation into the casing.
 29. The shaped charge of claim 28, wherein the asymmetrical feature is the liner being tilted relative the symmetry axis X so that one side of the liner touches the case at a first height and the other side of the liner touches the case at a second height, different from the first height.
 30. The shaped charge of claim 29, wherein the channel and the booster material are symmetrically distributed relative to the symmetry axis X.
 31. The shaped charge of claim 28, wherein the asymmetrical feature is that the symmetry axis X and an axis of symmetry X′ of the liner make a non-zero angle.
 32. The shaped charge of claim 28, wherein the asymmetrical feature is that the channel has a longitudinal axis X″, which makes a non-zero angle with the symmetry axis X.
 33. The shaped charge of claim 32, wherein the case, the explosive material and the liner are symmetrical relative to the symmetry axis.
 34. The shaped charge of claim 32, wherein the channel is offset relative to the symmetry axis.
 35. The shaped charge of claim 28, further comprising: another channel formed in the back wall of the case.
 36. The shaped charge of claim 35, wherein the another channel and the channel are asymmetrically located relative to the symmetry axis X.
 37. The shaped charge of claim 28, wherein the asymmetrical feature is that the booster material fires along an axis that is not the symmetry axis X.
 38. The shaped charge of claim 28, wherein the asymmetrical feature is that the booster material fires toward a side wall of the case.
 39. The shaped charge of claim 28, wherein the asymmetrical feature is that a first volume of the explosive material has a characteristic that is different from a second volume of the explosive material.
 40. The shaped charge of claim 39, wherein the characteristic is a density.
 41. The shaped charge of claim 39, wherein the characteristic is a chemical composition.
 42. The shaped charge of claim 28, wherein the asymmetrical feature is an insert placed inside the case.
 43. The shaped charge of claim 42, wherein the insert is fully embedded into the explosive material. 44-68. (canceled) 